1. Field of the Invention
The invention relates to a method for determining a buffer effect of an activated carbon filter for a tank venting system of a fuel container for hydrocarbon-containing fuels. The invention also relates to a test bench and a hydrocarbon feed system for a test bench for determining a buffer effect of an activated carbon filter.
2. Description of the Related Art
Vehicles that have an internal combustion engine for burning hydrocarbon-containing fuels also have a tank venting system with an activated carbon filter between a corresponding fuel container and the surroundings. The activated carbon filter stores hydrocarbons, but must be regenerated periodically by an air flow under the control of an engine electronics system. In this context, air supplied to the activated carbon filter releases hydrocarbon molecules and transports those molecules to the engine. Hydrocarbon molecules in this air flow mix with the combustion air and are burned in the engine.
The tank venting system is intended to avoid an excess pressure in a fuel tank of a motor vehicle, for example in the event of the vehicle being subjected to increased solar radiation in the deactivated state. The activated carbon filter in the tank venting system prevents hydrocarbons from passing from the tank into the surroundings when pressure equalization is necessary. The air flow typically is sucked in by an underpressure in the intake manifold of the engine and functions as a scavenging gas that is fed with the released hydrocarbons to combustion spaces of the engine.
Modern internal combustion engines have an exhaust-gas-side lambda controller, and an increased hydrocarbon content in the fresh gas can disadvantageously affect the engine controller. The scavenging gas flow for regenerating the activated carbon filter therefore has to be set selectively so that only a comparatively small hydrocarbon quantity is fed to the fresh gas of the engine, with this quantity ideally being known or compensated for by the engine controller. A buffer effect can be detected during the scavenging of the activated carbon filter that is loaded with hydrocarbon molecules since the embedded hydrocarbon molecules are not all simultaneously given up to the scavenging gas, but instead are released gradually in the course of a scavenging gas flow process which lasts for a relatively long time. The scavenging gas flow should be as small as possible to avoid disadvantageous effects at the engine controller. At the same time, the scavenging gas flow should be as large as possible so that the regeneration of the activated carbon filter can be carried out as quickly and completely as possible to prepare the tank venting system for the next stationary state of the vehicle. The attempt to find an optimum scavenging gas flow generally fails due to the fact that the buffer effect of the respective activated carbon filter can be determined only with difficulty and is different for each type of activated carbon filter.
An object of the invention is to determine the corresponding buffer effect directly and comparatively easily for any type of activated carbon filter.